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polish: feedback entry points on every surface (Linux About link, README, site) #419

Job	Run time
Racket core (contract tests)	1m 57s
macOS host (arm64 build)	4m 59s
Windows host (WinRT build)	5m 3s
Linux host (GTK4 build)	7m 0s
Contract preflight (i18n + release metadata)	5s
macOS host (x64 build)	11m 8s
	30m 12s